Direct access storage devices (DASDs), also referred to as disk drives or files, store information on concentric tracks of a rotatable magnetic recording disk. One or more disks are mounted on a spindle shaft connected to a spindle motor. A magnetic head or transducer element is moved from track to track on a disk to record and read the desired information. Typically a plurality of disks are stacked on one spindle shaft with a plurality of read/write heads positioned over the disk surfaces such that each surface of the disk has a corresponding head. Each head is attached to one of a plurality of suspensions which in turn are attached to a plurality of actuator arms which are connected to a rotary actuator or are an integral part of a rotary actuator comb. The actuator moves the heads in a radial direction across the disks. The heads, suspensions, arms and actuator comprise an actuator assembly. The disk, spindle and motor comprise a disk stack assembly. The disk stack assembly and actuator assembly are sealed in an enclosure, referred to as a disk or device enclosure. The device enclosure comprises a cover and a base plate. The disk stack assembly and actuator assembly are mounted on the base plate of the device enclosure.
An operating disk drive can emit relatively large amounts of acoustic noise generated by vibrations of the disk drive cover caused by the spinning motions of the spindle and seek and track following motions of the actuator. The spindle and actuator movements create forces that act on the structure of the disk drive. These forces eventually find a path to the device enclosure. When the forces reach the device enclosure, the forces are converted into displacements which in turn create pressure waves in the surrounding air which are perceived as acoustic noise to the human ear.
The device enclosure actually acts like a speaker for the internal forces created by the spindle and actuator movement. The dynamics of the device enclosure, such as the natural modes of vibration, act as mechanical amplifiers for the forces generated inside the drive. It has been found that the shape of the acoustic spectrum in the frequency domain is similar to the shape of the mechanical transfer function of the device enclosure. If it were possible to make the device enclosure infinitely stiff then no displacements could be created that would be manifested as acoustic noise.
Acoustic noise emanating from a disk drive is a critical performance factor that is usually tightly specified to be below a maximum level. As part of the quality assurances practices when manufacturing disk drives, the drives are tested in an acoustic tester to determine the amount of noise emanating from the device. Drives that emit noise above a maximum threshold need to be re-worked to be in compliance with the requirements. The re-working of disk drives consumes time and money which adds to the overall manufacturing costs for a disk drive unit.
Various schemes have been used in the prior art to modify the dynamics of the device enclosure to reduce the acoustic noise. For example, constrained layer dampers have been attached to disk drives. This method involves attaching a piece of sheet metal acting as a constraining layer to the cover and/or base of the device enclosure with a relatively thick layer of visco-elastic material between the sheet metal and cover and/or base. The visco-elastic material acts as a damper. However, constrained layer dampers are relatively expensive and add parts and complexity to the disk drive file assembly process.
U.S. Pat. No. 5,214,549 to Baker et al discloses a disk drive assembly having a cover with an additional plate and damping material between the plate and the cover in order to reduce acoustic noise. The damping layer damps acoustic vibrations imparted to the cover by the internally disposed components.
U.S. Pat. No. 5,282,100 to Tacklind et al discloses a disk drive having an outer cover for the drive which fits over an inner cover with raised plateaus in the inner cover and holes in the outer cover for accommodating the raised portion of the inner cover. Sound dampening material is placed between the inner and outer cover.
U.S. Pat. No. 5,235,482 to Schmitz discloses placing a gasket around the periphery where the cover and the base come into contact in order to reduce vibration and acoustic noise and provide greater damping of mechanical resonance in the disk drive. Additionally, a layer of damping material is inserted between the base assembly and circuit board assembly.
U.S. Pat. No. 5,079,655 to Yagi discloses a system for absorbing external or internal vibrations or shocks that may adversely affect a disk drive. The occurrence of a vibration while the drive is in operation may cause a head to be moved out of line with the required track resulting in an operation error. To protect the magnetic disk apparatus from such vibrations, a structure in the form of an external frame supporting the housing is used to absorb the vibration. Dampers are disposed vertically and horizontally between the exterior frame and the housing.
As greater emphasis is placed on simpler disk drive designs and ease of construction to reduce the cost of a disk drive assembly, there is a need for a scheme to sufficiently control the amount of acoustic noise emitted from a disk drive which does not add excessive cost or materials to the construction of the disk drive. As greater emphasis is also being placed on the size of the disk drive assembly system there is a need to reduce the noise without using much of the limited space in the disk assembly or increasing the overall size of the disk drive assembly.
The prior art systems have draw backs in increasing the complexity of the manufacturing processes, increasing the size, and increasing the number of parts used in the disk drive system.